1. Field of the Invention
This invention relates to a bearing plate for use with a mine roof bolt, and more particularly, to a bearing plate which includes a continuous elliptical embossment having a pair of straight portions extending along the side walls of the plate with the ends thereof joined by curved portions adjacent the end walls of the plate.
2. Description of the Prior Art
In underground mining, it is well known to provide support for mine roofs by means of a mine roof bolts extending in and anchored to bore holes in the mine roof with bearing plates extending around a portion of the mine roof bolt projecting from the bore hole. The mine roof bolt is anchored in the bore hole by mechanical means, resin or a combination of the two, and the mine roof anchor bolt is torqued in the bore hole after anchorage is achieved with the resultant effect of tensioning the bearing plate against the area of the mine roof adjacent the bore hole.
Various types of header plates having different configurations are known.
Generally, bearing plates have apertures at the midpoint of the plate, bearing surfaces for abutment against the mine roof, and another surface opposite the bearing surface from which extend embossments.
U.S. Pat. No. 4,037,418, U.S. Pat. No. RE B1 4,037,418, U.S. Pat. No. 4,095,430 and U.S. Pat. No. 4,095,431 disclose an embossment concentrically disposed around the midpoint of the bearing plate and having extensions therefrom extending toward the plate end walls.
U.S. Pat. No. 4,249,835 discloses a rectangular bearing plate with embossments extending longitudinally along the longer walls and centering ribs extending adjacent the aperture.
U.S. Pat. No. 4,371,293 discloses a bearing plate with an embossment concentrically disposed around the aperture, supporting rib type embossments extending therefrom toward the corners of the bearing plate, and embossments extending between the ribs adjacent the sides of the plate.
U.S. Pat. No. 4,445,808 discloses a bearing plate having a circular inner surface surrounded by a square outer surface around the aperture with the sides of the square inner surface parallel to the sides of the bearing plate. The embossment extends from the square outer surface upwardly toward the circular inner surface which is spaced from the opposite surface of the bearing plate. The circular inner surface includes an aperture in the bearing plate.
U.S. Pat. No. 4,498,815 discloses a bearing plate having embossments extending along opposite sides thereof, and aperture and embossments between the longitudinally extending embossments on either side of the aperture.
U.S. Pat. No. 4,507,020 discloses a rectangular bearing plate having embossments on either side of the aperture at the midpoint, and rods extending in longitudinally extending grooves adjacent the end parallel to the long sides of the rectangle.
U.S. Pat. No. 4,518,282 and U.S. Pat. No. 4,746,248 disclose a generally square bearing plate having an embossment concentrically disposed around the aperture at the midpoint thereof.
Although the prior art discloses bearing plates including various embossed areas or portions, there is a need for an improved bearing plate having a continuous embossment around the perimeter thereof to reinforce the bearing plate and to prevent buckling of the plate when subjected to the tension on the bolt head. There also remains a need for a bearing plate having a continuous embossment around the outer perimeter thereof such that stresses are transferred away from a localized stress point to the other portions of the continuous embossment due to the continuous configuration of the embossed area around the perimeter of the bearing plate to provide a bearing plate with increased resistance to localized stresses.